GPS position tracking method with variable updating rate for power conservation

ABSTRACT

A system and method in which the position update rate is adaptively modified, based on previous position measurements. By adjusting the update rate based on velocity predictions from two or more position fixes, a lower update rate may be used without exceeding the maximum error. Lowering the update rate reduces power consumption in the UE, providing longer battery operation. The updating method may comprise periodically repeating the velocity prediction and periodically adjusting the update rate responsive thereto. The update rate may be adjusted using additional information such as an acceleration prediction, a minimum update rate, or a preferred error. In some embodiments a model for user movement may be used to provide more accurate predictions, for example, stationary, walking, jogging, city driving, and freeway driving. The updating method may comprise receiving user input regarding the maximum position error.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

The present Application for Patent claims priority to U.S. patentapplication Ser. No. 11/083,419, filed Mar. 17, 2005, assigned to theassignee hereof and hereby expressly incorporated by reference herein.

BACKGROUND

1. Field

This disclosure relates to position tracking systems that use wirelesssignals to determine the location of user equipment, such as GPS andA-GPS systems.

2. Related Art

Mobile communication devices (generally termed “user equipment” or “UE”)have become an everyday part of modern life. Cell phones, particularly,have become ubiquitous, to such an extent that some people are foregoingconventional telephone service in favor of their cell phones.

In addition to their communication capabilities, some cell phones nowhave the capability of determining the position of the user equipment,taking advantage of satellite positioning systems (SPS) and/or the knownlocation of cellular base stations. Specifically, cell phones may berequired to have some positioning capabilities in order to facilitateemergency response to 911 calls; in addition, some cell phones canrespond to a user request for determining position. Whatever the reason,the increasing importance of position location services has encourageddevelopment of rapid, high sensitivity methods for acquiring the signalsused to determine position.

Position location technologies typically utilize wireless positioningsignals concurrently transmitted from known locations. In GPS systems,the positioning signals are concurrently transmitted from a multiplicityof satellites at a known time, with a predefined frequency. On theground, a GPS receiver acquires a positioning signal from each satellitewithin its view of the sky. The times of arrival of the positioningsignals along with the exact location of the in-view satellites and theexact times the signals were transmitted from each satellite are used totriangulate the position of the GPS receiver.

When a SPS fix is made, it gives the position at the time the GPSsignals are received. If, however, the GPS receiver is moving, it may bedesirable to regularly update position. For example, if a user hasrequested directions to a location, it may be desirable to monitor theposition of the UE in order to accurately pinpoint its approximatecurrent location, and thereby more accurately direct the user to theintended destination. In such a circumstance, it is desirable to monitorposition of the UE in real time as much as possible.

In order to monitor position of the UE over a period of time, the UE canmake a series of GPS position fixes. Typically these position fixes areperformed at a fixed, predetermined update rate, which may for examplebe at the maximum possible rate (e.g., immediately after a position fixis completed, the next position fix begins). Unfortunately, updating atthe maximum possible rate can consume system resources and slowoperation of the UE. Furthermore, reducing power consumption is animportant issue for those portable devices which carry a battery, andupdating the GPS position at the maximum possible update rate can drawsignificant power, which will reduce time before recharging will berequired. For example, if a battery can store 600 mAHr, and acontinuously-updating position location system consumes 45 mA per hour,then the battery would be completely consumed in about thirteen hours bythe position location system alone. However, if the fixed update ratewere to be reduced substantially to save power, then the update rate maynot be sufficient to accurately track position, especially if the userequipment is moving quickly.

Generally, because power consumption is an important issue for portabledevices such as mobile phones, any reduction in power consumption canadvantageously reduce drain on battery power, thereby extending batterylife, allowing battery size to be reduced, or both. For a user, anextended battery life allows more calls and position locations to bemade before recharging is required. If battery size is reduced, aportable device can be made smaller, more lightweight, and can bemanufactured at a lower cost.

SUMMARY

A system and method is disclosed in which the position update rate isadaptively modified, based on previous position measurements. Forexample, if the user is moving slowly, the position update rate can bereduced, but if the user moving faster such as in a car, the update ratewould be increased as more distance is being covered in a shorter periodof time. By updating the position fix based on velocity calculated fromtwo or more position fixes, the lowest possible update rate could beused. This reduces power consumed by an RF and BB digital receiver,thereby allowing longer application times for a given battery.

Particularly, a method is described for efficiently updating theposition of mobile wireless user equipment (UE) to reduce the rate ofenergy consumption. The method includes establishing an update rate fordetermining position, which defines the time delay between subsequentmeasurements, and selecting a maximum error in position. A velocityprediction is made for the UE, including making a series of at least twoposition fixes at the update rate, estimating the distance between atleast two of the position fixes, and determining the time differencebetween the two position fixes, and responsive to the time differenceand the estimated distance, calculating the velocity prediction of theUE. The update rate is adjusted responsive to the velocity prediction,including reducing the update rate to reduce power consumption withoutexceeding the maximum error in position. The update rate may also beincreased as appropriate to reduce the possibility that the maximumerror will not be exceeded. A series of position fixes are made at theadjusted update rate, thereby efficiently utilizing energy stored in theUE. The updating method may comprise periodically repeating the velocityprediction and periodically adjusting the update rate responsivethereto.

The update rate may be adjusted using information in addition to avelocity prediction. For example the updating method may furthercomprise making an acceleration prediction, and adjusting the updaterate responsive to the acceleration prediction. Also, the updatingmethod may comprise establishing a minimum update rate, and adjustingthe update rate so that it remains above or equal to the minimum updaterate. The updating method may also comprise establishing a preferrederror, and adjusting the update rate responsive to the preferred error.

In some embodiments a model for user movement may be used to providemore accurate predictions. For example the updating method may furthercomprise determining a model for user movement responsive to the seriesof position fixes, and adjusting the update rate responsive to themovement model and the velocity prediction. The movement model may, forexample, comprise one of stationary, walking, jogging, city driving, andfreeway driving.

The updating method may comprise receiving user input regarding themaximum position error, and determining the maximum position errorresponsive thereto. This user input may be provided, for example via akeypad or touch screen. The user input may be initiated by the user,such as by changing settings in the UE; alternatively, the user inputmay be received in response to a UE-initiated query.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a communication and position location system thatincludes satellites emitting GPS signals that are received by a GPSreceiver in UE that is in communication with a plurality of basestations.

FIG. 2 is a block diagram of one UE embodiment, including a GPS receiverand a cellular communication system.

FIG. 3 is a diagram illustrating the known position of the UE, themaximum error in position, and the movement of the UE resulting fromdifferent velocity assumptions, assuming that the UE will be travelingin a straight line at a constant velocity.

FIG. 4 is a diagram of an automobile in motion from left to right,showing the position of the automobile at a series of four positions.

FIG. 5 is a flowchart of operations that include adjusting the updaterate to efficiently update the UE's position.

FIG. 6 is a diagram illustrating a known position of the UE, the maximumerror in position, the preferred error in position, and the path of theUE in three different examples in which the UE is not traveling in astraight line and has a velocity that varies over time.

FIG. 7 is a diagram of an automobile in motion from left to right,showing the position of the automobile at a series of four positions.

FIG. 8 is a flowchart of operations to efficiently update the positionof UE that includes selection of a model for user movement and its usein adjusting the update rate.

FIG. 9 is a graph showing a relationship between update rate andvelocity to maintain a maximum error of about 10 m.

FIG. 10 is a graph showing a relationship between update rate andvelocity to maintain a maximum error of about 30 m.

FIG. 11 is a graph showing relationships between vehicle speed, timebetween updates, and time interval, as an example of UE movement inwhich the update rate is adjusted adaptively as described herein, usinga 30 m maximum error.

In the various figures of the drawing, like reference numbers representthe same or similar elements or parts.

DETAILED DESCRIPTION Glossary of Terms and Acronyms

The following terms and acronyms are used herein:

A-GPS: Assisted GPS. A location technology in which assistance to a GPSacquisition process is provided by a location server to reduceacquisition time and improve sensitivity.

Base Station: Base Transceiver Station or BTS. A fixed station used forcommunicating with user equipment. Includes antennas for transmittingand receiving wireless communication signals.

BB: base band.

CDMA: Code Division Multiple Access.

DFT: Discrete Fourier Transform

GPS: Global Positioning System. A system of satellites around the Earththat broadcast radio signals from which positions can be determined GPStypically refers to the U.S. Global Positioning System.

SPS: Satellite Positioning System. SPS is used generically to includeGPS as well as other global positioning systems, such as the RussianGlonass System, the planned European Galileo System, and the like.

SPS fix: The end result of a process of measurements and subsequentcomputations by which the location of the SPS user is determined.

GSM: Global System for Mobile, another widely-used digital wirelesstechnology.

mA: milliampere.

mAHr: milliampere per hour.

MS: Mobile Station, such as a cell phone that has a baseband modem forcommunicating with one or more base stations.

PCS: Personal Communication System.

PDE: Position Determination Entity. A system resource (e.g., a server)typically within the CDMA network, working in conjunction with one ormore GPS reference receivers, capable of exchanging GPS-relatedinformation with UE. In a UE-Assisted A-GPS session, the PDE can sendGPS assistance data to the UE to enhance the signal acquisition process.The UE can return information such as pseudorange measurements back tothe PDE, which is then capable of computing the position of the UE. In aUE-Based A-GPS session, the UE can send computed position results to thePDE.

RF: radio frequency.

SV: satellite vehicle. One major element of the Global PositioningSystem is the set of SV's orbiting the Earth and broadcasting uniquelyidentifiable signals.

UE: User Equipment. Any type of wireless communications device used by auser. Includes cellular, cordless, Personal Communication System (PCS),or other types of wireless telephone devices, pagers, wireless personaldigital assistants, notebook computers with wireless access, or anyother wireless mobile device, two-way radios, walkie-talkies, or othertype of communications transceiver, or mobile stations (MS), regardlessof whether or not they have valid SIM or USIM identifiers. UEs of thetype referenced in this disclosure typically include a GPS receiver.

Update Rate: As used herein, the update rate is the rate at whichposition location operations (position fixes) are performed. By itsperiod, the update rate defines the time delay between position fixes.

A system is described herein in which the subsequent position of UE ispredicted based upon information from two or more position locationfixes. From this, the position update rate is adjusted to provideacceptable tracking with a reduced number of position fix updates,thereby reducing current requirements and prolonging battery life.

Below is an overview of a GPS system and mobile station in which thissystem can be implemented, and following that is a detailed descriptionof the invention. For illustrative purposes, the embodiments herein aredescribed in terms of the current U.S. GPS System. However, theprinciples and embodiments herein may be applied to a variety of SPSsystems that utilize similar signaling formats, as well as to futurevariations of the U.S. GPS System.

Reference is now made to FIGS. 1 and 2. FIG. 1 illustrates a GPSenvironment that includes a plurality of GPS satellites (SV's) 11 thatemit GPS positioning signals 12, a plurality of land-based base stations10, and user equipment (UE). The US may be, for example, a cellulartelephone 14, a vehicle 13, or the like. The base stations 10 areconnected to a cellular infrastructure network 15, which allows it tocommunicate with other networks and communication systems, such as aphone system 16, computer networks 17 a, such as the internet, and othercommunication systems 17 b. The base stations 10 may comprise part of acommunication network that may include a number of additionalcommunication systems in communication with the base stations.

The UE 14 is described elsewhere herein, for example with reference toFIG. 2, but generally includes a GPS receiver and a two-waycommunication system for communication with the base stations usingtwo-way communication signals 20. Although the embodiments describedherein are primarily directed to cellular telephones or wirelesscommunication devices, it should be apparent that the GPS receiver couldbe implemented in a wide variety of other types of UE that communicatewith one or more base stations.

In FIG. 1, the UE 14 is illustrated as a hand-held device, although itmay have any suitable implementation, such as a built-in device in avehicle, such as an automobile 13. The UE 14 may be carried by a userwho is standing, walking, traveling in a car, or on publictransportation, for example. The UE 14 may be carried in the car 13 asit travels on its journey. It should be apparent that the user equipmentmay be positioned in a wide variety of environments, and may bestationary or moving.

The GPS satellites (SV's) 11 comprise any group of satellitesbroadcasting signals that are utilized for positioning a GPS receiver.Particularly, the satellites are synchronized to send wirelesspositioning signals 12 in phase with GPS time. These positioning signalsare generated at a predetermined frequency and in a predeterminedformat. In a current GPS implementation, each SV transmits a civiliantype of GPS signal on the L1-frequency band (at 1575.42 MHz) in a formatthat is in accordance with GPS standards.

When the GPS signals are detected by a conventional GPS receiver in theUE 14, the GPS system attempts to calculate the amount of time that haselapsed from transmission of the GPS signal until its reception at theUE. In other words, the GPS system calculates the time required for eachof the GPS signals to travel from their respective satellites to the GPSreceiver. The pseudo range is defined as: c·(T_(user)−T_(sv))+cT_(bias),where c is the speed of light, T_(user) is the GPS time when the signalfrom a given SV is received, T_(sv) is the GPS time when the satellitetransmitted the signal and T_(bais) is an error in the local user'sclock, normally present in the GPS receiver. Sometimes pseudorange isdefined with the constant “c” omitted. In the general case, the receiverneeds to resolve four unknowns: X, Y, Z (the coordinates of the receiverantenna), and T_(bias). For this general case, resolving the fourunknowns usually requires measurements from four different SV's;however, under certain circumstances, this constraint can be relaxed.For example, if an accurate altitude estimate is available, then thenumber of SV's required can be reduced from four to three. In so-calledassisted GPS operation, T_(sv) is not necessarily available to thereceiver and instead of processing true pseudoranges, the receiverrelies primarily upon code phases. In a current GPS implementation, thecode phases have one-millisecond time ambiguities, since the PN codesrepeat every one millisecond. Sometimes the data bit boundaries may beascertained, thus producing only 20-millisecond ambiguities.

The base stations 10 comprise any collection of base stations utilizedas part of a communication network that communicates with the UE 14using wireless signals 20. The base stations are connected to thecellular infrastructure network 15, which provides communicationservices with a plurality of other communication networks, such as apublic phone system 16, computer networks 17 a such as the internet, aposition determination entity (PDE) 18 (defined above), or a variety ofother communication systems, shown collectively in block 17 b. A GPSreference receiver (or receivers) 19, which may be in or near the basestations 10, or in any other suitable location, communicates with thePDE 18 to provide useful information in determining position, such as SVposition, or ephemeris, data.

The ground-based cellular infrastructure network 15 typically providescommunication services that allow the user of a cell phone to connect toanother phone over the phone system 16; however, the base stations couldalso be utilized to communicate with other devices or for othercommunication purposes, such as an internet connection with a handheldpersonal digital assistant (PDA). The base stations 10 may be, forexample, a part of a GSM communication network, a part of a synchronous(e.g., CDMA2000) or asynchronous communication network, or the like.

FIG. 2 is a block diagram of one embodiment of the mobile device 14,which includes communication and position location systems. A cellularcommunication system 22 is connected to an antenna 21 that communicatesusing the cellular signals 20. The cellular communication system 22comprises suitable devices, such as a modem 23, hardware, and softwarefor communicating with and detecting signals 20 from base stations, andprocessing transmitted or received information.

A GPS position location system 27 in the UE is connected to a GPSantenna 28 to receive positioning signals 12 that are transmitted at ornear the ideal GPS (carrier) frequency. The GPS system 27 comprises aGPS receiver 29 that includes frequency translation circuitry and ananalog-to-digital converter, a GPS clock, control logic to control thedesired functions of the GPS receiver, and suitable hardware andsoftware for receiving and processing GPS signals and for performing anycalculations necessary to determine position using a suitable positionlocation algorithm.

In the illustrated embodiment, the analog to digital converter isconnected to the buffer memory in the position location system, and abuffer memory is coupled to the DFT circuitry to provide and store thedata during the DFT operation. In some assisted GPS implementations thefinal position location calculations (e.g., latitude and longitude) areperformed at a remote server such as the position determination entity(PDE), based upon code phases and other information sent from the GPSreceiver to the remote server. Some examples of GPS systems aredisclosed in U.S. Pat. Nos. 5,841,396; 6,002,363; and 6,421,002; byNorman F. Krasner.

A mobile device control system 25 is connected to both the two-waycommunication system 22 and the position location system 27. The mobiledevice control system 25 includes any appropriate structure, such as oneor more microprocessors, memory, other hardware, firmware, and softwareto provide appropriate control functions for the systems to which it isconnected. It should be apparent that the processing steps describedherein are implemented in any suitable manner using hardware, software,or firmware, subject to control by the microprocessor.

The control system 25 is also connected to a user interface 26, whichincludes suitable components to interface with the user, such as akeypad, a microphone/speaker for voice communication services, adisplay, for example, a backlit LCD display, or the like. The mobiledevice control system 25 and user interface 26, connected to theposition location system 27 and two-way communication system 22, providesuitable input-output functions for the GPS receiver and the two-waycommunication system, such as controlling user input and displayingresults.

Reference is now made to FIGS. 3, 4, and 5 in which one system isdescribed in which the subsequent position of the UE is predicted basedupon information from two or more position location fixes. From this,the position update rate is adjusted to provide acceptable tracking witha reduced number of position fix updates, thereby reducing currentrequirements and prolonging battery life.

FIG. 3 is a diagram illustrating the currently known position of the UE31, the maximum acceptable error in position 32, and the movements 33-36of the UE resulting from different velocity assumptions, assuming thatthe UE will be traveling in a straight line at a constant velocity forpurposes of simplicity of description. In FIG. 3, the currently knownposition of the UE is shown at 31 in the center of an error circle 32,which defines the maximum acceptable error in position. The maximumerror is determined in any suitable manner. For example, the maximumerror may be predetermined, it may depend upon location, it may beselected by user input, any combination of these, or the like.

As can be seen in FIG. 3, any movement of the UE in a straight linemoves away from its known position, and toward the maximum error 32 at arate determined by the velocity of the UE. Several examples are shown aslines 33-36 emanating from the center, each line representing thepositional movement of the UE at different velocity. Each line 33-36includes a number of vectors, each vector indicating the distance thatthe UE will travel in one time unit (tu). At the first positional line33, which assumes a first velocity, approximately four and one-half timeunits (4.5 tu) will elapse before the maximum error is reached. At thesecond positional line 34, which assumes a second, faster velocity,approximately three and one-half time units (3.5 tu) will elapse beforethe maximum error is reached. At the third positional line 35, whichassumes a third, still faster velocity, approximately two andone-quarter time units (2.25 tu) will elapse before the maximum error isreached. At the fourth positional line 36, which assumes a fourth, muchfaster velocity, less than one time unit, approximately four-fifths of atime unit (0.8 tu), will elapse before the maximum error is reached.

Conventionally, the update rate is fixed. If we assume that each timeunit, tu, represents one period of a fixed update rate, then from FIG.3, it can be seen that this particular fixed update rate will provideacceptable information for the first, second, and third velocityassumptions (shown at 33, 34, and 35), but at the expense of the powerloss resulting from an unnecessary number of position fixes. However,for the fourth velocity assumption (shown at 36), the fixed rate is notadequate, because the UE has traveled beyond the boundaries defined bythe maximum error.

FIG. 4 is a diagram of an automobile in motion from left to right,showing the position of the automobile at a series of four positions 41,42, 43, and 44. The distances (X0, X1, X2, and X3) correspond to theseposition fixes, and the time elapsed between these position fixes isshown as T1, T2, and T3. FIG. 4 is used to illustrate how a velocityprediction can be made based upon at least two of these position fixes,and the time difference between when these position fixes were made. Itmay be noticed that FIG. 4 is a simplified, one-dimensional view ofmovement, and is provided for purposes of illustration. A more complexmodel is described hereinbelow.

The velocity prediction can be made in many different ways. Onestraightforward method is to take the distance between two positionmeasurements, and divide that distance by the time necessary to crossthat distance. For example, the distance from X0 to X1 can be divided bythe time T1 to get a velocity prediction for the subsequent time period.As another example, the distance from X0 to X2 can be divided by the sumof T1 and T2 to get a velocity prediction for a subsequent time period.As another example, velocity estimates over two or more periods may beaveraged to arrive at the next velocity prediction.

If desired, an acceleration prediction may be made in addition to thevelocity prediction. For example, the acceleration prediction may becalculated responsive to changes in velocity over a series ofmeasurements, such as an average over a number of measurements, such asthe most recent three, five, ten, or other number of measurements.Depending upon the application, a greater weight may be given to themost recent changes in velocity, upon the assumption that theacceleration at the present moment is likely to be most closely relatedto the acceleration in the most recent moment.

FIG. 5 is a flowchart of operations to efficiently update the positionof mobile wireless user equipment (UE), while reducing the rate ofenergy consumption. As used herein, the update rate is the rate at whichposition location operations (position fixes) are performed. By itsperiod, the update rate defines the time delay between position fixes.

At 51, an initial update rate for determining position is established.This initial update rate is determined in any suitable way. For examplethe initial update rate may be predetermined, it may be at the maximumpossible rate, it may relate to the most recent update rate used by theparticular UE, or it may relate to another suitable technique.

At 52, a maximum error in position is established. This maximum error isdiscussed above with reference to FIG. 3 and may be selected in anysuitable matter. For example, the maximum error may be predetermined, itmay depend upon location, it may be selected by user input, orcombination of thereof.

At 53, a preferred error may be established. The preferred error may beestablished with consideration of user preferences and target powerconsumption. An example of a preferred error is shown in FIG. 6 andappears as a concentric circle 63 within the maximum error circle 62.

At 54, a velocity prediction for the UE is established. The velocityprediction is described in more detail in conjunction with FIG. 4. InFIG. 5, for illustration purposes, the steps shown include making aseries of at least two position fixes at the update rate and estimatingthe distance between at least two of the position fixes. Thus, thevelocity prediction of the UE may be calculated responsive to thecalculated time delay and the estimated travel distance.

In some embodiments, an acceleration prediction may be made in additionto the velocity prediction. For example, the acceleration prediction maybe calculated responsive to changes in velocity over a series ofmeasurements, such as an average over the last four measurements. Agreater weight may be given to the most recent changes in velocity.

At 55, responsive to the velocity prediction and the maximum error inposition, and possibly also to the acceleration prediction, the updaterate is adjusted to reduce power consumption while still providing themaximum error in position. More particularly, adjusting the update rateincludes reducing the update rate to reduce power consumption withoutexceeding the maximum error in position. This may also includeincreasing the update rate as appropriate to stay within a predeterminedrange from the maximum allowable error.

For example, at a higher velocity, the update rate is adjusted toincrease the number of measurements to follow the faster rate of changeof position in order to provide the same maximum error. Conversely, at aslower velocity, the update rate can be reduced to conserve power whilestill providing the same maximum error. The predicted velocity may beused directly. One example might be to simply assume that the UE willtravel approximately at the predicted velocity and then adjust theupdate rate accordingly. However, a more conservative approach would beto adjust the update rate to some fraction of the velocity in order toaccount for the possibility that the UE may speed up. For example, theupdate rate may be adjusted assuming that the UE will travel at twicethe predicted velocity in order to make it more likely that the maximumerror will not be exceeded.

In addition to the velocity prediction and the maximum error, a numberof factors may be considered when adjusting the update rate. Forexample, the preferred error (discussed with respect to block 53, supra)may be useful to adjust the update rate. Furthermore, a floor, orminimum, update rate may be implemented to avoid adjusting the updaterate to too low a level; for example, if the UE is temporarily stopped,such as at a traffic light, or moving relatively slowly. The floor, orminimum, update rate may be established in any suitable way.

In addition, the accuracy of GPS measurements may be considered whenadjusting the update rate. For example, a less accurate GPS measurementmay require a higher update rate in order to maintain the same maximumerror. Conversely a more accurate GPS measurement may advantageouslyallow a lower update rate.

At 56, a position fix is made at the adjusted update rate, therebyefficiently utilizing energy stored in the UE.

At 57, a decision is made as to whether or not to repeat theprediction(s), such as the velocity prediction, with more recentposition information and the adjusted update rate. This decision may bebased upon any of a number of factors. A simple approach would be toperiodically repeat the velocity prediction after a specified lapse oftime or a certain number of position fixes. Another approach is to takeinto account the observed changes of velocity over a number of previousposition fixes, and repeat the velocity prediction accordingly. Thus, ifthe observed changes are significant, then the velocity predictionshould be repeated more often, but if the observed changes are notsignificant, then the velocity prediction may be repeated lessfrequently.

Reference is now made to FIGS. 6, 7, and 8 to describe a more complexsystem in which the subsequent position of the UE is predicted basedupon information from two or more position location fixes. In order toassist in making a more accurate prediction of position, a model isselected that approximately matches the movement (for example, walking,jogging, stationary, freeway driving, and stop-and-go city driving) ofthe UE over a number of recent position fixes. Using this user movementmodel, the position update rate is adjusted to provide more accurateposition tracking with a reduced number of position fix updates, therebyreducing current requirements and prolonging battery life.

FIG. 6 is a diagram illustrating a known position of the UE, the maximumerror in position, the preferred error in position, and the path of theUE in three different examples. The FIG. 6 embodiment assumes a “realworld” situation in which the UE may be not be traveling in a straightline, and may have a velocity that varies over time. In FIG. 6, theknown position of the UE is shown at 61 in the center of an error circle62. The circle 62 defines the maximum acceptable error in position.

The maximum error is determined in any suitable manner. For example, themaximum error may be predetermined, it may depend upon location, it maybe selected by user input, it may be selected in another suitablemanner, or combination of thereof. In addition, FIG. 6 shows a“preferred error” in the form of a circle around the known position. Thepreferred error may be established with consideration of userpreferences and target power consumption.

Three example paths are shown in FIG. 6, each representing one type ofmovement. Each path is shown as a group of connected vectors emanatingfrom the center. Each vector indicates the distance that the UE travelsin one time unit (tu). It may be noted that many variations of movementare possible, and a movement model can be developed for each. Thesethree examples are provided only for purposes of illustration.

As can be seen from the examples of FIG. 6, the paths of the UE areusually in a direction away from its known position, although this doesnot always have to be true. For example, the UE may move back towardsits previous position.

At a first path 64, the UE zigzags away from the center known position,as if the UE is driving or walking on city streets. Eventually the path63 arrives at the maximum error 62, but only after about 7.2 time units(7.2 tu). This type of path can define a city driving model.

At a second path 65, the UE travels at a greater velocity than in thefirst path 64, and therefore travels a greater distance between turns.This type of path can define a suburban, or rural driving model.

At a third path 66, the UE travels in an approximately straight line ata greater velocity than the first or second paths. This type of path candefine a freeway driving model.

FIG. 7 is a diagram of an automobile in motion from left to right,showing the position of the automobile at a series of four positions 71,72, 73, and 74. A corresponding fix is made at each of these positionsat (X0, Y0; X1, Y1; X2, Y2; and X3, Y3), and time elapsed between theseposition fixes (T1, T2, and T3). FIG. 7 is used to illustrate how aposition prediction can be made based upon at least two of theseposition fixes and the time difference between when these position fixeswere made.

In comparison with FIG. 4, FIG. 7 is a two-dimensional view of movementthat provides a more complex model than one-dimensional movement shownin FIG. 1; however, even a two-dimensional view is simplified from thethree-dimensional movement of a real UE. Therefore, it should be clearthat FIG. 7 is provided for purposes of illustration.

In the context of FIGS. 6 and 7, the velocity prediction is notnecessarily the instantaneous velocity. Instead it is the velocity froma recent known position (shown in the center in FIG. 6), since it is thedistance from the recent known position that is relevant to determiningthe update rate to stay within the maximum error. Determining thevelocity prediction from the center known position can be made in manydifferent ways. One straightforward method is to take the directdistance from the center, and divide that distance by the time necessaryto cross that distance. For example, in FIG. 7, the first and fourthpositions are the same distance from the y-axis, and therefore define adirect line from the center. Accordingly, the distance from X0 to Y0 toX3 to Y3 can be divided by the sum of the times T1, T2 and T3 to get avelocity prediction for the subsequent time period. As another example,in FIG. 6 a vector 75 shows the distance from the center known positionto the actual position after two time periods. This distance can bedivided by two to give the velocity from center.

FIG. 8 is a flowchart of operations to efficiently update the positionof mobile wireless user equipment (UE), while reducing the rate ofenergy consumption. At 81, an initial update rate for determiningposition is established. This initial update rate is determined in anysuitable way, for example it may be predetermined, it may be at themaximum possible rate, or it may relate to the most recent update rateused by the particular UE.

At 82, a maximum error in position is established. This maximum error isdiscussed above with reference to FIGS. 3 and 6, for example. Themaximum error may be predetermined, it may depend upon location, it maybe selected by user input, selected in any suitable manner, or anycombination of these.

At 83, a preferred error may be established as discussed with referenceto 63 in FIG. 6.

At 84, making a velocity prediction from a previously known position ofthe UE is shown. The velocity prediction is described in more detailwith reference to FIGS. 6 and 7. In FIG. 8, for illustration purposes,the steps shown include making a series of at least two position fixesat the update rate, and estimating the distance from center to theendpoint of the latest position fix. Responsive to the elapsed time andthe distance from the center, a velocity prediction of the UE iscalculated.

In some embodiments, an acceleration prediction may be made in additionto the velocity. For example, the acceleration prediction may becalculated responsive to changes in velocity over a series ofmeasurements, such as an average over the last four measurements. Agreater weight may be given to the most recent changes in velocity.

At 85, the path is examined to select an appropriate model for movementof the UE. For example if the path resembles the first path 64, then themodel of city driving is selected, if the path resembles the second path65, then the model of suburban driving selected, and if the pathresembles the third path 66, then the model of freeway driving isselected.

At 86, the update rate is adjusted in response to the velocityprediction, the selected model, and the maximum error in position.Adjusting the update rate includes reducing the update rate to reducepower consumption, without exceeding the maximum error in position.Adjusting the update rate also includes increasing the update rate asappropriate to stay within a predetermined range from the maximumallowable error. For example, at a higher velocity, the update rate maybe adjusted to increase the number of measurements to follow the fasterrate of change of position in order to provide the same maximum error.Conversely, at a slower velocity, the update rate can be reduced toconserve power while still providing the same maximum error.

The predicted velocity may be used directly. One example is to simplyassume that the UE will travel approximately at the predicted velocity,and then adjust the update rate accordingly. However, a moreconservative approach is to adjust the update rate to some fraction ofthe velocity in order to account for the possibility that the UE mayspeed up. For example, the update rate may be adjusted, assuming thatthe UE will travel at twice the predicted velocity, in order to make itmore likely that the maximum error will not be exceeded.

In addition to the velocity prediction and the maximum error, a numberof factors may be considered when adjusting the update rate. Forexample, the acceleration prediction or the preferred error may beuseful to adjust the update rate. Furthermore, a floor, or minimum,update rate may be implemented to avoid adjusting the update rate toolow. The floor, or minimum, update rate may be established in anysuitable way to avoid adjusting the update rate too low, for example, ifthe UE is temporarily stopped, such as at a traffic light, or movingrelatively slowly.

At 87, a position fix is made at the adjusted update rate, therebyefficiently utilizing energy stored in the UE.

At 88, a decision is made as to whether or not to repeat the velocityprediction or to reselect the model, using more recent positioninformation and the adjusted update rate. This decision may be basedupon any of a number of factors and methodologies. A simple approach isperiodical. For example, the velocity prediction may periodically repeatafter a specified lapse of time or a certain number of position fixes.Another approach is to take into account the observed changes ofvelocity over a number of previous position fixes, and repeat thevelocity prediction accordingly. For example, if the observed changesare significant, then the velocity prediction should be repeated moreoften, but if the observed changes are not significant, then thevelocity prediction may be repeated less frequently.

FIGS. 9 and 10 are graphs that show examples of one way in which theupdate rate can be adjusted responsive to the predicted velocity tomaintain a maximum error and reduce power consumption. In FIG. 9, a plotline 91 shows a graph of the seconds/update (the period between updates)as a function of predicted velocity, for a maximum error of 10 m. InFIG. 10 a plot line 101 shows a graph of the seconds/update as afunction of predicted velocity, for a maximum error of 30 m.

The following Table 1 sets forth the data and information used to createthe graph lines shown in FIGS. 9 and 10. In the following Table 1, thethird and fourth columns show the update as “seconds/update” (i.e., theperiod). It should be clear that the update rate can be obtainedstraightforwardly from this value by taking the inverse.

TABLE 1 update adjustment example Seconds/update Seconds/update SpeedDistance traveled in (10 m max error) (30 m max error) (mph) 1 sec (ft)(91, FIG. 9) (101, FIG. 10) 1 1.47 22.39 67.16 10 14.67 2.24 6.72 1116.13 2.04 6.11 12 17.60 1.87 5.60 13 19.07 1.72 5.17 18 26.40 1.24 3.7323 33.73 0.97 2.92 28 41.07 0.80 2.40 33 48.40 0.68 2.04 38 55.73 0.591.77 43 63.07 0.52 1.56 48 70.40 0.47 1.40 53 77.73 0.42 1.27 58 85.070.39 1.16 63 92.40 0.36 1.07 68 99.73 0.33 0.99 73 107.07 0.31 0.92 78114.40 0.29 0.86

As can be seen, the velocity is inversely related to the time betweenupdates. A higher predicted velocity requires more frequent updates.

FIG. 11 is an example of adjusting the update rate adaptively, using a30 m maximum error as an example. In FIG. 11, the predicted velocity isplotted as a solid line 111 (in units of mph), and the time/update isplotted as a dashed line 112 (in units of seconds/update). The data andcalculations for this example are shown in the table below, for eachsuccessive position location determination shown in column 1 Note thatthe maximum number of seconds per update (at zero mph) is set at tenseconds in this example.

TABLE 2 Example of adaptively adjusting the update rate PositionDistance traveled in Seconds per number Speed(mph) 1 sec (ft) update 1 00.00 10.00 2 10 14.67 6.72 3 20 29.33 3.36 4 40 58.67 1.68 5 40 58.671.68 6 10 14.67 6.72 7 20 29.33 3.36 8 30 44.00 2.24 9 40 58.67 1.68 1050 73.33 1.34 11 60 88.00 1.12 12 60 88.00 1.12 13 40 58.67 1.68 14 2029.33 3.36 15 0 0.00 10.00 16 0 0.00 10.00 17 10 14.67 6.72 18 20 29.333.36 19 30 44.00 2.24 20 30 44.00 2.24

Therefore it can be seen how the update rate can be adjusted to adapt tothe predicted velocity of the UE.

It will be appreciated by those skilled in the art, in view of theseteachings, that alternative embodiments may be implemented withoutdeviating from the spirit or scope of the invention. This invention isto be limited only by the following claims, which include all suchembodiments and modifications when viewed in conjunction with the abovespecification and accompanying drawings.

The invention claimed is:
 1. A method for efficiently updating theposition of mobile wireless user equipment (UE) to reduce the rate ofenergy consumption, comprising: establishing an update rate fordetermining position; making a velocity prediction for said UE;adjusting said update rate responsive to said velocity prediction and atarget power consumption; and making a series of position fixes at saidadjusted update rate.
 2. The method of claim 1, further comprisingperiodically repeating said velocity prediction and periodicallyadjusting said update rate responsive thereto.
 3. The method of claim 1,further comprising making an acceleration prediction and adjusting saidupdate rate responsive to said acceleration prediction.
 4. The method ofclaim 1, further comprising establishing a minimum update rate andadjusting said update rate to at least said minimum update rate.
 5. Themethod of claim 1, further comprising determining a model for usermovement responsive to said series of position fixes, and furtheradjusting said update rate responsive to said movement model and saidvelocity prediction.
 6. The method of claim 5, wherein said movementmodel comprises one of stationary, walking, jogging, city driving, andfreeway driving.
 7. The method of claim 1, further comprisingestablishing a preferred error and adjusting said update rate responsiveto said preferred error and said maximum error.
 8. The method of claim1, further comprising receiving user input regarding a maximum positionerror and determining said maximum position error responsive thereto. 9.The method of claim 1, wherein said step of making said velocityprediction for said UE comprises: making a series of at least twoposition fixes at said update rate; estimating a distance between atleast two of said position fixes; determining a time difference betweensaid two position fixes; and responsive to said time difference and saidestimated distance, calculating said velocity prediction of said UE. 10.The method of claim 1, wherein said step of adjusting said update rateresponsive to said velocity prediction comprises reducing said updaterate to reduce power consumption without exceeding a maximum positionerror.
 11. The method of claim 1, wherein said step of adjusting saidupdate rate comprises increasing said update rate to follow a fasterpredicted velocity without exceeding a maximum position error.
 12. Asystem for efficiently updating the position of mobile wireless userequipment (UE) to reduce the rate of energy consumption, comprising:means for establishing an update rate for determining position; meansfor making a velocity prediction for said UE; means for adjusting saidupdate rate responsive to said velocity prediction and a target powerconsumption; and means for making a series of position fixes at saidadjusted update rate.
 13. The system of claim 12, further comprisingmeans for periodically repeating said velocity prediction, and means forperiodically adjusting said update rate responsive thereto.
 14. Thesystem of claim 12, further comprising means for making an accelerationprediction, and means for adjusting said update rate responsive to saidacceleration prediction.
 15. The system of claim 12, further comprisingmeans for establishing a minimum update rate, and means for adjustingsaid update rate to at least said minimum update rate.
 16. The system ofclaim 12, further comprising means for determining a model for usermovement responsive to said series of position fixes, and means forfurther adjusting said update rate responsive to said movement model andsaid velocity prediction.
 17. The system of claim 16, wherein saidmovement model comprises one of stationary, walking, jogging, citydriving, and freeway driving.
 18. The system of claim 12, furthercomprising means for establishing a preferred error, and means foradjusting said update rate responsive to said preferred error and saidmaximum error.
 19. The system of claim 12, further comprising means forreceiving user input regarding a maximum position error, and means fordetermining said maximum position error responsive thereto.
 20. Thesystem of claim 12, wherein said means for making said velocityprediction for said UE comprises: means for making a series of at leasttwo position fixes at said update rate; means for estimating a distancebetween at least two of said position fixes; means for determining atime difference between said two position fixes; and means, responsiveto said time difference and said estimated distance, for calculatingsaid velocity prediction of said UE.
 21. The system of claim 12, whereinsaid means for adjusting said update rate responsive to said velocityprediction comprises means for reducing said update rate to reduce powerconsumption without exceeding a maximum position error.
 22. The systemof claim 12, wherein said means for adjusting said update rate comprisesmeans for increasing said update rate to follow a faster predictedvelocity without exceeding a maximum position error.
 23. A method forefficiently updating the position of mobile wireless user equipment (UE)to reduce the rate of energy consumption, comprising: establishing anupdate rate for determining position; making a velocity prediction forsaid UE; adjusting said update rate responsive to said velocityprediction and a location of said UE; and making a series of positionfixes at said adjusted update rate.
 24. The method of claim 23, furthercomprising periodically repeating said velocity prediction andperiodically adjusting said update rate responsive thereto.
 25. Themethod of claim 23, further comprising making an acceleration predictionand adjusting said update rate responsive to said accelerationprediction.
 26. The method of claim 23, further comprising establishinga minimum update rate and adjusting said update rate to at least saidminimum update rate.
 27. The method of claim 23, further comprisingdetermining a model for user movement responsive to said series ofposition fixes and further adjusting said update rate responsive to saidmovement model and said velocity prediction.
 28. The method of claim 27,wherein said movement model comprises one of stationary, walking,jogging, city driving, and freeway driving.
 29. The method of claim 23,further comprising establishing a preferred error and adjusting saidupdate rate responsive to said preferred error and said maximum error.30. The method of claim 23, further comprising receiving user inputregarding a maximum position error and determining said maximum positionerror responsive thereto.
 31. The method of claim 23, wherein said stepof making said velocity prediction for said UE comprises: making aseries of at least two position fixes at said update rate; estimating adistance between at least two of said position fixes; determining a timedifference between said two position fixes; and responsive to said timedifference and said estimated distance, calculating said velocityprediction of said UE.
 32. The method of claim 23, wherein said step ofadjusting said update rate responsive to said velocity predictioncomprises reducing said update rate to reduce power consumption withoutexceeding a maximum position error.
 33. The method of claim 23, whereinsaid step of adjusting said update rate comprises increasing said updaterate to follow a faster predicted velocity without exceeding a maximumposition error.
 34. A system for efficiently updating the position ofmobile wireless user equipment (UE) to reduce the rate of energyconsumption, comprising: means for establishing an update rate fordetermining position; means for making a velocity prediction for saidUE; means for adjusting said update rate responsive to said velocityprediction and a location of said UE; and means for making a series ofposition fixes at said adjusted update rate.
 35. The system of claim 34,further comprising means for periodically repeating said velocityprediction and means for periodically adjusting said update rateresponsive thereto.
 36. The system of claim 34, further comprising meansfor making an acceleration prediction and means for adjusting saidupdate rate responsive to said acceleration prediction.
 37. The systemof claim 34, further comprising means for establishing a minimum updaterate and means for adjusting said update rate to at least said minimumupdate rate.
 38. The system of claim 34, further comprising means fordetermining a model for user movement responsive to said series ofposition fixes, and means for further adjusting said update rateresponsive to said movement model and said velocity prediction.
 39. Thesystem of claim 38, wherein said movement model comprises one ofstationary, walking, jogging, city driving, and freeway driving.
 40. Thesystem of claim 34, further comprising means for establishing apreferred error, and means for adjusting said update rate responsive tosaid preferred error and said maximum error.
 41. The system of claim 34,further comprising means for receiving user input regarding a maximumposition error, and means for determining said maximum position errorresponsive thereto.
 42. The system of claim 34, wherein said means formaking said velocity prediction for said UE comprises: means for makinga series of at least two position fixes at said update rate; means forestimating a distance between at least two of said position fixes; meansfor determining a time difference between said two position fixes; andmeans, responsive to said time difference and said estimated distance,for calculating said velocity prediction of said UE.
 43. The system ofclaim 34, wherein said means for adjusting said update rate responsiveto said velocity prediction comprises means for reducing said updaterate to reduce power consumption without exceeding a maximum positionerror.
 44. The system of claim 34, wherein said means for adjusting saidupdate rate comprises means for increasing said update rate to follow afaster predicted velocity without exceeding a maximum position error.45. Apparatus for updating the position of mobile wireless userequipment (UE), comprising: processing circuitry configured to establishan update rate for determining position; the processing circuitryfurther configured to make a velocity prediction for said UE; theprocessing circuitry further configured to adjust said update rateresponsive to said velocity prediction and a target power consumption;and the processing circuitry further configured to make a series ofposition fixes at said adjusted update rate.
 46. The apparatus of claim45, the processing circuitry further configured to periodically repeatsaid velocity prediction and periodically adjust said update rateresponsive thereto.
 47. The apparatus of claim 45, the processingcircuitry further configured to make an acceleration prediction andadjust said update rate responsive to said acceleration prediction. 48.The apparatus of claim 45, the processing circuitry further configuredto establish a minimum update rate and adjust said update rate to atleast said minimum update rate.
 49. The apparatus of claim 45, theprocessing circuitry further configured to determine a model for usermovement responsive to said series of position fixes, and further adjustsaid update rate responsive to said movement model and said velocityprediction.
 50. The apparatus of claim 49, wherein said movement modelcomprises one of stationary, walking, jogging, city driving, and freewaydriving.
 51. The apparatus of claim 45, the processing circuitry furtherconfigured to establish a preferred error and adjust said update rateresponsive to said preferred error and said maximum error.
 52. Theapparatus of claim 45, the processing circuitry further configured toreceive user input regarding a maximum position error and determine saidmaximum position error responsive thereto.
 53. The apparatus of claim45, wherein said processing circuitry that is further configured to makesaid velocity prediction for said UE comprises: processing circuitryconfigured to make a series of at least two position fixes at saidupdate rate; the processing circuitry further configured to estimate adistance between at least two of said position fixes; the processingcircuitry further configured to determine a time difference between saidtwo position fixes; and the processing circuitry further configured tocalculate said velocity prediction of said UE, responsive to said timedifference and said estimated distance.
 54. The apparatus of claim 45,wherein said processing circuitry that is further configured to adjustsaid update rate responsive to said velocity prediction comprisesprocessing circuitry configured to reduce said update rate to reducepower consumption without exceeding a maximum position error.
 55. Theapparatus of claim 45, wherein said processing circuitry that is furtherconfigured to adjust said update rate comprises processing circuitryconfigured to increase said update rate to follow a faster predictedvelocity without exceeding a maximum position error.
 56. Anon-transitory processor-readable storage medium storing a program thatwhen executed on a processor of a device, causes the processor toperform a method of updating the position of mobile wireless userequipment (UE), the method comprising: establishing an update rate fordetermining position; making a velocity prediction for said UE;adjusting said update rate responsive to said velocity prediction and atarget power consumption; and making a series of position fixes at saidadjusted update rate.
 57. Apparatus for updating the position of mobilewireless user equipment (UE), comprising: processing circuitryconfigured to establish an update rate for determining position; theprocessing circuitry further configured to make a velocity predictionfor said UE; the processing circuitry further configured to adjust saidupdate rate responsive to said velocity prediction and a location ofsaid UE; and the processing circuitry further configured to make aseries of position fixes at said adjusted update rate.
 58. The apparatusof claim 57, the processing circuitry further configured to periodicallyrepeat said velocity prediction and periodically adjust said update rateresponsive thereto.
 59. The apparatus of claim 57, the processingcircuitry further configured to make an acceleration prediction andadjust said update rate responsive to said acceleration prediction. 60.The apparatus of claim 57, the processing circuitry further configuredto establish a minimum update rate and adjust said update rate to atleast said minimum update rate.
 61. The apparatus of claim 57, theprocessing circuitry further configured to determine a model for usermovement responsive to said series of position fixes, and further adjustsaid update rate responsive to said movement model and said velocityprediction.
 62. The apparatus of claim 61, wherein said movement modelcomprises one of stationary, walking, jogging, city driving, and freewaydriving.
 63. The apparatus of claim 57, the processing circuitry furtherconfigured to establish a preferred error and adjust said update rateresponsive to said preferred error and said maximum error.
 64. Theapparatus of claim 57, the processing circuitry further configured toreceive user input regarding a maximum position error and determine saidmaximum position error responsive thereto.
 65. The apparatus of claim57, wherein said processing circuitry that is further configured to makesaid velocity prediction for said UE comprises: processing circuitryconfigured to make a series of at least two position fixes at saidupdate rate; the processing circuitry further configured to estimate adistance between at least two of said position fixes; the processingcircuitry further configured to determine a time difference between saidtwo position fixes; and the processing circuitry further configured tocalculate said velocity prediction of said UE, responsive to said timedifference and said estimated distance.
 66. The apparatus of claim 57,wherein said processing circuitry that is further configured to adjustsaid update rate responsive to said velocity prediction comprisesprocessing circuitry configured to reduce said update rate to reducepower consumption without exceeding a maximum position error.
 67. Theapparatus of claim 57, wherein said processing circuitry that is furtherconfigured to adjust said update rate comprises processing circuitryconfigured to increase said update rate to follow a faster predictedvelocity without exceeding a maximum position error.
 68. Anon-transitory processor-readable storage medium storing a program thatwhen executed on a processor of a device, causes the processor toperform a method of updating the position of mobile wireless userequipment (UE), the method comprising: establishing an update rate fordetermining position; making a velocity prediction for said UE;adjusting said update rate responsive to said velocity prediction and alocation of said UE; and making a series of position fixes at saidadjusted update rate.